Ultrathin Bi2Te3 single crystals laid on Scotch tape are
investigated by Fourier transform infrared spectroscopy at 4K and in a
magnetic field up to 35T. The magneto-transmittance spectra of the Bi2%
Te3/tape composite are analyzed as a two-layer system and the optical
conductivity of Bi2Te3 at different magnetic fields are extracted. We
find that magnetic field modifies the optical conductivity in the following
ways: (1) Field-induced transfer of the optical weight from the lower frequency
regime (<250cm−1) to the higher frequency regime (cm−1) due
to the redistribution of charge carriers across the Fermi surface. (2) Evolving
of a Fano-resonance-like spectral feature from an anti-resonance to a resonance
with increasing magnetic field. Such behavior can be attributed to the
electron-phonon interactions between the optical phonon mode and
the continuum of electronic transitions. (3) Cyclotron resonance resulting from
the inter-valence band Landau level transitions, which can be described by the
electrodynamics of massive Dirac holes